package network;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

//回显服务器
public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    public void start() throws IOException {
        System.out.println("服务器启动!");
        while (true){

            //1.读取请求,并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);
            String request =  new String(requestPacket.getData(),0,requestPacket.getLength());
            //2.根据请求,计算出相应
            String response = process(request);
            //3.把相应写回客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),0,response.getBytes().length,requestPacket.getSocketAddress());
            socket.send(responsePacket);

            System.out.printf("[%s:%d] req: %s, resp: %s\n", requestPacket.getAddress().toString(), requestPacket.getPort(),
                    request, response);

        }
    }

    public String process(String request){
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }

}

/*package network;

        import java.io.IOException;
        import java.net.DatagramPacket;
        import java.net.DatagramSocket;
        import java.net.SocketException;

// UDP 的 回显服务器.
// 客户端发的请求是啥, 服务器返回的响应就是啥.
public class UdpEchoServer {
    private DatagramSocket socket = null;

    // 参数是服务器要绑定的端口
    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    // 使用这个方法启动服务器.
    public void start() throws IOException {
        System.out.println("服务器启动!");
        while (true) {
            // 反复的, 长期的执行针对客户端请求处理的逻辑.
            // 一个服务器, 运行过程中, 要做的事情, 主要是三个核心环节.
            // 1. 读取请求, 并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096], 4096);
            socket.receive(requestPacket);
            //    这样的转字符串的前提是, 后续客户端发的数据就是一个文本的字符串.
            String request = new String(requestPacket.getData(), 0, requestPacket.getLength());
            // 2. 根据请求, 计算出响应
            String response = process(request);
            // 3. 把响应写回给客户端
            //    此时需要告知网卡, 要发的内容是啥, 要发给谁.
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(), response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);
            // 记录日志, 方便观察程序执行效果.
            System.out.printf("[%s:%d] req: %s, resp: %s\n", requestPacket.getAddress().toString(), requestPacket.getPort(),
                    request, response);
        }
    }

    // 根据请求计算响应. 由于是回显程序, 响应内容和请求完全一样.
    public String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}*/
